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Building a Relational Data Model

In This Chapter
Building a Data Model
Overview of the Entity-Relationship Data Model
Identifying and Defining Principal Data Objects
Discovering Entities
Choosing Possible Entities
The List of Entities
Telephone Directory Example
Diagramming Entities
Defining the Relationships
Connectivity
Existence Dependency
Cardinality
Discovering the Relationships
Diagramming Relationships
Identifying Attributes
Selecting Attributes for Entities
Listing Attributes
About Entity Occurrences
Diagramming Data Objects
Reading E-R Diagrams
Telephone Directory Example
After the Diagram Is Complete
Translating E-R Data Objects into Relational Constructs
Defining Tables, Rows, and Columns
Placing Constraints on Columns
Domain Characteristics
Determining Keys for Tables
Primary Keys
Foreign Keys (Join Columns)
Adding Keys to the Telephone Directory Diagram
Resolving Relationships
Resolving m:n Relationships
Resolving Other Special Relationships
Normalizing a Data Model
First Normal Form
Second Normal Form
Third Normal Form
Summary of Normalization Rules
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